Instabilities of the metal surface in electrolytic alumina reduction cells

Transient waves on the metal surface in electrolytic cells are studied by simulation on a computer model. The model used is a semidynamic modification of a model for stationary flow and surface calculation.The simulation results clearly show that any wave once started by some disturbance, will turn into a transient wave rotating along the edge of the cell cavity, resulting in a tilting movement of the whole metal surface. The mechanism of the rotating wave is explained.It is further demonstrated that there exists a stability limit above which the rotating waves are amplified instead of being damped, leading to an unstable situation known as “shaky pot”. A simple empirical stability formula is presented, showing the interrelation of the decisive cell parameters. General estimation curves for typical cells are also given.